Forming processes are used to make large and/or structural glass fiber reinforced composite (GFRC) parts. Such processes include RIM (Reactive Injection Molding), SRIM (Structural Reactive Injection Molding), RTM (Resin Transfer Molding), VARTM (Vacuum Assisted Resin Transfer Molding), SMC (Sheet Molding Compound), BMC (Bulk Molding Compound), spray-up forming, filament winding, LFI (Long Fiber Injection molding) and pultrusion.
In injection molding processes, chopped glass fibers, and/or flakes and/or particles of stabilizing filler, and/or coloring pigments and pellets of a thermoplastic polymeric resin are fed into an extruder mix the two together at elevated temperature and maceration due to the high viscosity of the molten thermoplastic polymer(s) or copolymer(s). Substantial working and maceration is important and sometimes necessary to wet out the glass fibers at the elevated temperature due to the high viscosity, and as a result the glass fibers are shortened significantly. The resultant mixture is formed into a molding material that is supplied to a press or injection molding system to be formed with very expensive tooling into GFRC parts. During the extrusion process using single or twin-screw machines, the resin is heated and melted and the fibres are dispersed throughout the molten resin to form a fibre/resin mixture. Next, the fibre/resin mixture may be degassed, cooled, and formed into pellets or slugs. The dry fibre strand/resin dispersion pellets are then fed to a moulding machine and formed into moulded composite articles that have a substantially homogeneous dispersion of glass fibre strands throughout the composite article. Alternatively, in the process using continuous filaments, fibreglass filaments are mixed with the molten resin in an extruder with the screw geometry designed to mix the matrix with fibres without causing significant damage to the fibres. The resultant extruded mixtures are then compression molded to form long-fibre reinforced thermoplastic parts having superior mechanical properties due to the nature of the orientation and the longer length of the fibers. Because of these difficulties, the use of thermoplastics to make vehicle parts was very limited.
With the newly proposed challenging CAFE gas mileage standards being introduced, there is a larger than ever need for lighter weight vehicle parts that thermoplastic fiber reinforced composite (TPFRC) could satisfy, because TPFRC scrap is recyclable. The thermoplastic polymers or copolymers may be melted and reclaimed, and ground thermoplastic TPFRC may be used in thermoplastic forming processes including injection molding, extrusion, etc. Thus, there is a large need for TPFRC parts using normally thermoset processes including RIM, SRIM, RTM, VARTM, LFI, SMC, BMC, spray-up hand lay-up etc., and also improved materials for extrusion and for injection molding. Additionally, there is a need for materials that will undergo no, or a very minimum, branching or cross-linking polymerization during extrusion processing or in the injection molding equipment prior to entering and being formed in the mold(s). Currently, such tendency to form branching and/or cross-linking polymerization in these processes while in the extruder and/or in the injection molding system prior to the mold when using reactive materials causes increases in viscosity and shear resistance that is extremely costly if not prohibitive to the use of such reactive materials in these processes. Thus, there is a need for methods of polymerizing and forming thermoplastic polymers, copolymers and homopolymers in situ surrounding the fiber reinforcements in a mold.
Low viscosity caprolactam monomers, one containing an activator and another mixture containing a caprolactam monomer and a catalyst may be cast by mixing the two very low viscosity mixtures together prior to casting. However, this mixture may be kept to less than about 100° C. to prevent rapid polymerization. Following casting, the cast mixture is heated in the mold to cause anionic poylmerization of the monomer to produce a polyamide. However, this method is not practical for most vehicle and large parts and many other current thermoset parts because of the relatively low temperature limitation and the time delays that are caused in the forming and polymerizing cycle. If TPFRC is to replace metals or thermoset fiber reinforced composites (TSFRC) substantially in the automotive industry and elsewhere, economical method(s) need to be found that will produce such automotive parts of equal or superior performance at competitive costs with metal and TSFRC parts now in use. This and other challenges are addressed in the present application.